Encoder, motor with encoder, and servo system having a plurality of light receiving array to receive light reflected by slit tracks comprising incremental patterns and absolute pattern

ABSTRACT

An encoder includes a plurality of slit tracks, a point light source, a first light-receiving array, a second light-receiving array, and a third light-receiving array. The plurality of slit tracks respectively comprises a plurality of reflection slits arranged along a measurement direction. The point light source is configured to emit diffusion light to the plurality of slit tracks. The first light-receiving array is configured to receive light reflected by the slit track comprising an incremental pattern. The second light-receiving array is configured to receive light reflected by the slit track comprising an incremental pattern longer in pitch than other incremental patterns. The third light-receiving array is configured to receive light reflected by the slit track comprising an absolute pattern.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent ApplicationNo. 2013-229834, which was filed on Nov. 5, 2013, the disclosure ofwhich is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to an encoder, a motor with an encoder,and a servo system.

Description of the Related Art

A reflection type encode is known.

SUMMARY OF THE INVENTION

According to one aspect of the disclosure, there is provided an encodercomprising a plurality of slit tracks, a point light source, a firstlight-receiving array, a second light-receiving array, and a thirdlight-receiving array. The plurality of slit tracks respectivelycomprises a plurality of reflection slits arranged along a measurementdirection. The point light source is configured to emit diffusion lightto the plurality of slit tracks. The first light-receiving array isconfigured to receive light reflected by the slit track comprising anincremental pattern. The second light-receiving array is configured toreceive light reflected by the slit track comprising an incrementalpattern longer in pitch than other incremental patterns. The thirdlight-receiving array is configured to receive light reflected by theslit track comprising an absolute pattern.

According to another aspect of the disclosure, there is provided anencoder comprising a plurality of slit tracks, a point light source, afirst light-receiving array, a second light-receiving array, and onesubstrate. The plurality of slit tracks respectively comprises aplurality of reflection slits arranged along a measurement direction.The point light source is configured to emit diffusion light to theplurality of slit tracks. The first light-receiving array is configuredto receive light reflected by the slit track comprising an incrementalpattern. The second light-receiving array is configured to receive lightreflected by the slit track comprising an incremental pattern longer inpitch than other incremental patterns. The point light source, the firstlight-receiving array, and the second light-receiving array are disposedin the one substrate.

According to another aspect of the disclosure, there is provided anencoder comprising a plurality of slit tracks, means for emittingdiffusion light to the plurality of slit tracks, means for receivinglight reflected by the slit track comprising an incremental pattern,means for receiving light reflected by the slit track comprising anincremental pattern longer in pitch than other incremental patterns, andmeans for receiving light reflected by the slit track comprising anabsolute pattern. The plurality of slit tracks respectively comprises aplurality of reflection slits arranged along a measurement direction.

According to another aspect of the disclosure, there is provided a motorwith an encoder, comprising a linear motor or a rotary motor, and theabove-described encoder. A mover moves with respect to a stator in thelinear motor. A rotor rotates with respect to a stator in the rotarymotor. The encoder is configured to detect at least one of a positionand a velocity of the mover or the rotor.

According to another aspect of the disclosure, there is provided a servosystem comprising a linear motor or a rotary motor, the above-describedencoder, and a controller. A mover moves with respect to a stator in thelinear motor. A rotor rotates with respect to a stator in the rotarymotor. The encoder is configured to detect at least one of a positionand a velocity of the mover or the rotor. The controller is configuredto control the linear motor or the rotary motor based on a detectionresult of the encoder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view for explaining a servo system related toan embodiment.

FIG. 2 is an explanatory view for explaining an encoder related to theembodiment.

FIG. 3 is an explanatory view for explaining a disk related to theembodiment.

FIG. 4 is an explanatory view for explaining a slit track related to theembodiment.

FIG. 5 is an explanatory view for explaining an optical module and alight-receiving array related to the embodiment.

FIG. 6 is an explanatory view for explaining a position data generatingpart related to the embodiment.

FIG. 7 is an explanatory view for explaining an irregular reflectioncaused by an unevenness of the disk surface related to the embodiment.

FIG. 8 is an explanatory view for explaining a directivity of theirregular reflection components caused by convex parts.

FIG. 9 is an explanatory view for explaining an intensity distributionof the irregular reflection components as viewed from a positivedirection along an X axis.

FIG. 10 is an explanatory view for explaining an intensity distributionof the irregular reflection components as viewed from a positivedirection along a Z axis.

FIG. 11 is an explanatory view for explaining an optical module and alight-receiving array related to modification 1.

FIG. 12 is an explanatory view for explaining an optical module and alight-receiving array related to modification 2.

FIG. 13 is an explanatory view for explaining an optical module and alight-receiving array related to modification 3.

FIG. 14 is an explanatory view for explaining an optical module and alight-receiving array related to modification 4.

FIG. 15 is an explanatory view for explaining an optical module and alight-receiving array related to modification 5.

FIG. 16 is an explanatory view for explaining an optical module and alight-receiving array related to modification 6.

FIG. 17 is an explanatory view for explaining an optical module and alight-receiving array related to modification 7.

FIG. 18 is an explanatory view for explaining a slit track related tomodification 8.

FIG. 19 is an explanatory view for explaining an optical module and alight-receiving array related to modification 8.

FIG. 20 is an explanatory view for explaining an optical module and alight-receiving array related to modification 9.

FIG. 21 is an explanatory view for explaining an optical module and alight-receiving array related to modification 10.

FIG. 22 is an explanatory view for explaining an optical module and alight-receiving array related to modification 11.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following describes an embodiment with reference to accompanyingdrawings.

Note that the encoder related to the embodiment described hereinafter isapplicable to various types of encoders, such as a rotary type and alinear type. In the following, the embodiments are described using therotary-type encoder as an example to ensure ease of encoderunderstanding. In a case where the embodiments are to be applied toanother encoder type, it is possible to apply the type by addingappropriate changes, such as changing the object to be measured from arotary-type disk to a linear scale, and thus detailed descriptionsthereof are omitted.

1. Servo System

First, the configuration of a servo system related to this embodimentwill be described with reference to FIG. 1. As shown in FIG. 1, theservo system S comprises a servo motor SM and a controller CT. The servomotor SM comprises an encoder 100 and a motor M.

The motor M is an example of a power generation source not including theencoder 100. The motor M is a rotary-type motor in which a rotor (notshown) rotates with respect to a stator (not shown), and outputs arotational force by rotating a shaft SH fixed to the rotor around anaxis AX.

Further, the motor M alone is sometimes referred to as a servo motor,but, in this embodiment, the configuration including the encoder 100 isreferred to as the servo motor SM. That is, the servo motor SMcorresponds to one example of a motor with an encoder. The following,for convenience of explanation, describes a case where the motor with anencoder is a servo motor controlled so as to follow target values, suchas position and velocity values, but the motor is not necessarilylimited to a servo motor. In a case where the output of the encoder isused for display only, for example, the motor with an encoder alsoincludes motors used in a system other than a servo system, as long asan encoder is attached.

The motor M is not particularly limited as long as it is a motor inwhich the encoder 100 is capable of detecting position data and thelike, for example. Further, the motor M is not limited to an electricmotor that uses electricity as a power source, and it may be a motorthat uses, for example, another power source, such as a hydraulic motor,a pneumatic motor, and a steam motor. However, for convenience ofexplanation, the following describes a case where the motor M is anelectric motor.

The encoder 100 is connected to the side opposite the rotational forceoutput side of the shaft SH of the motor M. Note that the connected sideis not necessarily limited to the opposite side, allowing the encoder100 to be connected to the rotational force output side of the shaft SH.The encoder 100 detects a position of the motor M (also referred to as arotational angle) by detecting the position of the shaft SH (rotor), andoutputs position data representing the position.

The encoder 100 may detect at least one of a velocity of the motor M(also referred to as rotation speed, angular velocity, and the like) andan acceleration of the motor M (also referred to as rotationacceleration, angular acceleration, and the like) in addition to or inplace of the position of the motor M. In this case, the velocity and theacceleration of the motor M can be detected by, for example, obtainingthe first derivative or the second derivative of the position withrespect to time, or counting a detection signal (an incremental signaldescribed later, for example) for a predetermined period of time. Forconvenience of explanation, the following describes the embodiment withthe physical quantity detected by the encoder 100 as the position.

The controller CT acquires position data output from the encoder 100,and controls the rotation of the motor M based on the position data.Consequently, in this embodiment where an electric motor is used as themotor M, the controller CT controls the rotation of the motor M bycontrolling the current, voltage, or the like to be applied to the motorM based on position data. Furthermore, it is also possible for thecontroller CT to control the motor M by acquiring a master controlsignal from a master controller (not shown) so that a rotational forcecapable of achieving a position and the like represented by the mastercontrol signal is output from the shaft SH of the motor M. Note that, ina case where the motor M uses another power source, such as a hydraulic,pneumatic, or steam motor, it is possible for the controller CT tocontrol the rotation of the motor M by controlling the supply of thepower source.

2. Encoder

Next, the encoder 100 related to this embodiment will be described. Asshown in FIG. 2, the encoder 100 comprises a disk 110, an optical module120, and a position data generating part 130.

Here, for convenience of explanation of a structure of the encoder 100,directions, such as upward and downward directions, are defined andsuitably used as follows. In FIG. 2, the direction in which the disk 110faces the optical module 120, that is, the positive direction along theZ axis, is referred to as “upward” and the negative direction along theZ axis is referred to as “downward.” Note that the directions varyaccording to the attachment mode of the encoder 100, and the positionalrelationship of each configuration of the encoder 100 is not limited.

2-1. Disk

The disk 110 is formed into the shape of a circular plate as shown inFIG. 3, and disposed so that a disk center O substantially agrees withthe axis AX. The disk 110 is connected to the shaft SH of the motor M,and rotates by the rotation of the shaft SH. Note that, in thisembodiment, explanation is given with the disk 110 in the shape of acircular plate as an example of an object to be measured that measuresthe rotation of the motor M. However, it is also possible to use anothermember, such as an end surface of the shaft SH, for example, as anobject to be measured. Further, while the disk 110 is directly connectedto the shaft SH in the example shown in FIG. 2, the disk 110 may beconnected via a connecting member such as a hub.

As shown in FIG. 3, the disk 110 comprises a plurality of slit tracksSA, SI1, SI2. While the disk 110 rotates with the drive of the motor M,the optical module 120 is disposed fixedly while facing a portion of thedisk 110. Consequently, the slit tracks SA, SI1, SI2 and the opticalmodule 120 move relatively to each other in the measurement direction(the direction of arrow C shown in FIG. 3; hereinafter suitably referredto as “measurement direction C”) as the motor M is driven.

Here, the “measurement direction” is the measurement direction when therespective slit tracks formed on the disk 110 by the optical module 120are optically measured. In a rotary-type encoder in which the object tobe measured is the disk 110 as in this embodiment, the measurementdirection agrees with the circumferential direction with the center axisof the disk 110 as its center, but is the direction along a linear scalein a linear-type encoder in which the object to be measured is a linearscale and a mover moves with respect to a stator. Note that the “centeraxis” is the rotational axis of the disk 110, and agrees with the axisAX of the shaft SH in a case where the disk 110 and the shaft SH arecoaxially connected.

2-2. Optical Detecting Mechanism

The optical detecting mechanism comprises the slit tracks SA, SI1, SI2and the optical module 120. The respective slit tracks are formed astracks disposed in a ring shape with the disk center O as its center onthe upper surface of the disk 110. Each of the slit tracks comprises aplurality of reflection slits (the sections shaded by slashes in FIG. 4)arranged side by side across the entire circumference of the track alongthe measurement direction C. Each reflection slit reflects lightirradiated from a light source 121. Note that the light source 121corresponds to one example of means for emitting diffusion light to theplurality of slit tracks.

2-2-1. Disk

The disk 110 is formed by a material that reflects light, such as metal,for example. Then, a material with low reflectance (such as chromiumoxide, for example) is disposed onto sections where light is not to bereflected on the surface of the disk 110 by a coating process or thelike, thereby forming reflection slits in sections where the material isnot disposed. Note that the reflection slits may also be formed bycreating a coarse surface on the sections where light is not to bereflected by sputtering or the like, thereby reducing reflectance.

Further, the material, manufacturing method, and the like of the disk110 are not particularly limited. For example, the disk 110 may beformed using a material that transmits light, such as glass ortransparent resin. In this case, the reflection slits can be formed bydisposing a material that reflects light (such as aluminium, forexample) on the surface of the disk 110 by vapor deposition or the like.

Three slit tracks are arranged on the upper surface of the disk 110 inthe width direction (the direction of arrow R shown in FIG. 3;hereinafter suitably referred to as “width direction R”). Note that the“width direction” is the radial direction of the disk 110, i.e., thedirection substantially orthogonal to the measurement direction C, andthe length of each slit track along this width direction R correspondsto the width of each slit track. The three slit tracks areconcentrically disposed in the order of SA, SI1, SI2, from the insidetoward the outside in the width direction R. In order to explain therespective slit tracks in further detail, FIG. 4 shows a partiallyenlarged view of the vicinity of an area of the disk 110 facing theoptical module 120.

As shown in FIG. 4, a plurality of reflection slits sa included in theslit track SA is disposed along the entire circumference of the disk 110so as to comprise an absolute pattern in the measurement direction C.

Note that the “absolute pattern” is a pattern in which the positions,proportions, and the like of the reflection slits within an angle inwhich the light-receiving arrays of the optical module 120 describedlater face each other are uniquely defined within one rotation of thedisk 110. That is, for example, if the motor M is in a certain angularposition in the case of the example of the absolute pattern shown inFIG. 4, a combination of bit patterns resulting from detection ornon-detection by each of the plurality of light-receiving elements ofthe light-receiving arrays facing each other uniquely represents theabsolute position of the angular position. Note that the “absoluteposition” refers to an angular position with respect to the originwithin one rotation of the disk 110. The origin is set in a suitableangular position within one rotation of the disk 110, and the absolutepattern is formed with this origin as a reference.

Note that, according to an example of this pattern, it is possible togenerate a pattern that one-dimensionally represents the absoluteposition of the motor M by bits in the number of light-receivingelements of the light-receiving array. However, the absolute pattern isnot limited to this example. For example, the pattern may be a patternmulti-dimensionally represented by bits in the number of light-receivingelements. Further, other than a predetermined bit pattern, the patternmay be a pattern in which a physical quantity, such as a phase or amountof light received by the light-receiving elements, changes so as touniquely represent the absolute position, a pattern in which a codesequence of an absolute pattern modulates, or other various patterns.

On the other hand, a plurality of reflection slits si1, si2 respectivelyincluded in the slit tracks SI1, SI2 is disposed along the entirecircumference of the disk 110 so as to comprise an incremental patternin the measurement direction C.

The “incremental pattern” is a pattern repeated regularly at apredetermined pitch, as shown in FIG. 4. Here, “pitch” refers to thedisposed interval of the respective reflection slits si1, si2 of theslit tracks SI1, SI2 that comprise an incremental pattern. As shown inFIG. 4, the pitch of the slit track SI1 is P1, and the pitch of the slittrack SI2 is P2. The incremental pattern, unlike the absolute patternthat represents the absolute position by the bits corresponding todetection or non-detection by the plurality of light-receiving elements,represents the position of the motor M for each pitch or within onepitch by the sum of the detection signals resulting from at least one ormore of the light-receiving elements. Consequently, the incrementalpattern does not represent the absolute position of the motor M, but canrepresent the position with very high accuracy compared to the absolutepattern.

According to this embodiment, the pitch P1 of the slit track SI1 is setlonger than the pitch P2 of the slit track SI2. According to thisembodiment, each pitch is set so that P1=2×P2. That is, the number ofreflection slits si2 of the slit track SI2 is two times the number ofthe reflection slits si1 of the slit track SI1. Nevertheless, therelationship of this slit pitch is not limited to this example, and cantake various values, such as three times, four times, and five times,for example.

Note that, according to this embodiment, the minimum length of thereflection slit sa of the slit track SA in the measurement direction Cagrees with the pitch P1 of the reflection slit si1 of the slit trackSI1. As a result, the resolution of the absolute signal based on theslit track SA agrees with the number of the reflection slits si1 of theslit track SI1. Nevertheless, the minimum length is not limited to thisexample, and the number of the reflection slits si1 of the slit trackSI1 is preferably set greater than or equal to the resolution of theabsolute signal.

2-2-2. Optical Module

The optical module 120, as shown in FIG. 2 and FIG. 5, is formed as onesubstrate BA parallel to the disk 110. With this arrangement, theencoder 100 can be thinned and the structure of the optical module 120can be simplified. Consequently, the optical module 120 relatively moveswith respect to the slit tracks SA, SI1, SI2 in the measurementdirection C, accompanying the rotation of the disk 110. Note that theoptical module 120 does not necessarily need to be configured as onesubstrate BA, allowing each component to be configured as a plurality ofsubstrates. In this case, these substrates may be collectively disposed.Further, the optical module 120 does not need to be in the form of asubstrate.

The optical module 120, as shown in FIG. 2 and FIG. 5, comprises thelight source 121, and a plurality of light-receiving arrays PA, PI1, PI2on the surface of the substrate BA facing the disk 110.

As shown in FIG. 3, the light source 121 is disposed in a positionfacing the area between the slit track SI1 and the slit track SI2. Then,the light source 121 emits light onto the sections facing the three slittracks SA, SI1, SI2 that pass through the positions facing the opticalmodule 120.

The light source 121 is not particularly limited as long as it is alight source capable of irradiating the irradiation area with light,allowing use of a light emitting diode (LED), for example. The lightsource 121 is particularly configured as a point light source in whichno optical lens or the like is disposed, and emits diffusion light froma light-emitting part. Note that, when referring to a “point lightsource,” the light source does not need to be strictly a point, and thelight may be emitted from an emission surface comprising a finitesurface area as long as the light source is regarded as capable ofemitting diffusion light from a substantially point-like position fromthe standpoint of design and operation principles. Further, the“diffusion light” is not limited to light emitted from a point lightsource toward all directions, but includes light that is diffused andemitted toward a certain finite direction. That is, the term “diffusionlight” used here includes any light that comprises more diffusibilitythan parallel light. By using a point light source in this manner, it ispossible for the light source 121 to substantially uniformly irradiatethe three slit tracks SA, SI1, SI2 that pass through the positionsfacing thereto with light. Further, collecting and diffusing of light byan optical element are not performed, and therefore errors and the likecaused by the optical element are unlikely to occur, making it possibleto increase the straightness of light toward the slit tracks.

The plurality of the light-receiving arrays PA, PI1, PI2 is disposedalong the circumference of the light source 121, and comprises aplurality of light-receiving elements (the sections shaded by dots inFIG. 5), each which receives light reflected by the reflection slits ofthe slit tracks correspondingly associated thereto. The plurality oflight-receiving elements is arranged side by side along the measurementdirection C, as shown in FIG. 5.

Note that the light emitted from the light source 121 is diffusionlight. Consequently, the image of the slit tracks projected onto theoptical module 120 is an image magnified by a predetermined magnifyingpowers in accordance with the optical path length. That is, as shown inFIG. 4 and FIG. 5, given WSA, WSI1, WSI2 as the respective lengths ofthe slit tracks SA, SI1, SI2 in the width direction R and WPA, WPI1,WPI2 as the lengths of the shapes of the reflection light projected ontothe optical module 120 in the width direction R, WPA, WPI1, WPI2 arelengths corresponding to ε times WSA, WSI1, WSI2. Note that thisembodiment shows an example in which the lengths of the light-receivingelements of the respective light-receiving arrays in the width directionR are set substantially equal to the shape of the respective slitsprojected onto the optical module 120, as shown in FIG. 5. However, thelengths of the light-receiving elements in the width direction R are notnecessarily limited to this example.

Similarly, the measurement direction C in the optical module 120 is alsothe shape of the measurement direction C in the disk 110 projected ontothe optical module 120, that is, the shape affected by the magnifyingpower ε. In order to make understanding easier, the following provides adetailed explanation using the measurement direction C in the positionof the light source 121 as an example, as shown in FIG. 2. Themeasurement direction C in the disk 110 is circular in shape, with theaxis AX as a center. Conversely, the center of the measurement directionC projected onto the optical module 120 is located in a positionseparated from an optical center Op, which is in a position within theplane of the disk 110 on which the light source 121 is disposed, by adistance εL. The distance εt, is a distance L between the axis AX andoptical center Op magnified by the magnifying power ε. This position isconceptually illustrated in FIG. 2 as a measurement center Os.Consequently, the measurement direction C in the optical module 120 ison a line having the measurement center Os separated by the distance εLfrom the optical center Op on a line on which the optical center Op andthe axis AX are located in the direction of the axis AX as a center andthe distance εL as a radius.

In FIG. 4 and FIG. 5, the correspondence relationship of the measurementdirection C in the disk 110 and the optical module 120 is represented byarc-shaped lines Lcd, Lcp. The line Lcd shown in FIG. 4 represents aline on the disk 110 along the measurement direction C, and the line LCPshown in FIG. 5 represents a line on the substrate BA along themeasurement direction C (the line Lcd projected onto the optical module120).

As shown in FIG. 2, given G as a gap length between the optical module120 and the disk 110, and Δd as an amount of protrusion of the lightsource 121 from the substrate BA, the magnifying power ε is expressed bythe following (Formula 1).ε=(2G−Δd)/(G−Δd)  (Formula 1)

As each light-receiving element, a photodiode, for example, can be used.However, the light-receiving element is not limited to a photodiode andis not particularly limited as long as it is capable of receiving lightemitted from the light source 121 and converting the light into anelectric signal.

The light-receiving array in this embodiment is disposed correspondinglyto the three slit tracks SA, SI1, SI2. The light-receiving array PA isconfigured to receive the light reflected by the slit track SA. Further,the light-receiving array PI1 is configured to receive the lightreflected by the slit track SI1, and the light-receiving array PI2 isconfigured to receive the light reflected by the slit track SI2.

The light source 121, the light-receiving array PA, and thelight-receiving arrays PI1, PI2 are disposed in the positionalrelationship shown in FIG. 5. That is, the light-receiving arrays PI1,PI2 are disposed further on the direction side where the light source121 rather than the light-receiving array PA is disposed. Then, thelight source 121 is disposed between the light-receiving array PI1 andthe light-receiving array PI2. As a result, the light source 121 and therespective light-receiving arrays are disposed in the order of thelight-receiving array PI2, the light source 121, the light-receivingarray PI1, and the light-receiving array PA, from the outside toward theinside in the width direction R (from the outside toward the center axisof the circle).

The light-receiving array PA corresponding to the absolute patterncomprises two types of light-receiving arrays PA1, PA2. Light-receivingelements p1, p2 included in each of these light-receiving arrays PA1,PA2 are alternately disposed along the measurement direction C (lineLcp), configuring the two light-receiving arrays PA1, PA2 as thelight-receiving array PA of a single track. The light-receiving arraysPA1, PA2 respectively receive the reflection light from the slit trackSA, thereby generating an absolute signal comprising a bit pattern inthe number of light-receiving elements. Note that the light-receivingarray PA corresponds to one example of the third light-receiving array,and also to one example of means for receiving light reflected by theslit track comprising an absolute pattern.

In this example, the disposed pitch of the light-receiving element p1and the disposed pitch of the light-receiving element p2 both correspondto a minimum length (pitch P1) of the reflection slit sa of the slittrack SA in the measurement direction C (the minimum length of theprojected image; that is ε×P1), and the length of each of thelight-receiving elements p1, p2 in the measurement direction C agreeswith one-half of ε×P1. With this arrangement, the light-receiving arraysPA1, PA2 are offset against each other by a length equivalent toone-half of one bit in the measurement direction C (equivalent toone-half of the pitch P1). Note that the length of each of thelight-receiving elements p1, p2 in the measurement direction C is notlimited to the above, and may be a length other than one-half of ε×P1.

As a result, the following advantages are achieved. If thelight-receiving array PA were not to comprise the light-receiving arraysPA1, PA2 offset in the measurement direction, in other words, if thelight-receiving array PA were configured as one type of light-receivingarray comprising a plurality of light-receiving elements, possibilitiessuch as the following exist. That is, if the absolute position isrepresented by a one-dimensional absolute pattern such as in thisembodiment, the detection accuracy of the absolute position may decreasein the area of a change in the bit pattern resulting from the respectivelight-receiving elements of the light-receiving array PA beingpositioned facing the vicinity of an end area of the reflection slits.According to this embodiment, since the light-receiving arrays PA1, PA2are offset by a length equivalent to one-half of one bit, the absoluteposition is calculated using the detection signal from thelight-receiving array PA2 or the opposite operation is performed when,for example, the absolute position by the light-receiving array PA1corresponds to a change point in the bit pattern. As a result, it ispossible to improve the detection accuracy of the absolute position.Note that, while the amount of received light in the two light-receivingarrays PA1, PA2 needs to be uniform in the case of such a configuration,the two light-receiving arrays PA1, PA2 are disposed equidistant fromthe light source 121 according to this embodiment, making it possible toachieve the above described configuration.

The light-receiving array PI1 corresponding to the incremental patternis disposed between the light-receiving array PA and the light source121. Further, the light-receiving array PI2 corresponding to theincremental pattern is disposed on the outer circumference side of thelight source 121. The light-receiving array PI1 is disposed further onthe inner circumference side (the center axis side) than thelight-receiving array PI2. Further, the distances between each of thelight-receiving arrays PI1, PI2 and the light source 121 aresubstantially equal. That is, the light-receiving arrays PI1, PI2 arebasically formed into an axisymmetrical shape with the line on the widthdirection R and the line on the measurement direction C that passthrough the light source 121 as the axes of symmetry (excluding thecurved shape with the measurement center Os as the center). Note thatthe light-receiving array P12 corresponds to one example of the firstlight-receiving array, and also to one example of means for receivinglight reflected by the slit track comprising an incremental pattern.Further, the light-receiving array PI1 corresponds to one example of thesecond light-receiving array, and also to one example of means forreceiving light reflected by the slit track comprising an incrementalpattern that is longer in pitch than other incremental patterns.

This embodiment illustrates a one-dimensional pattern as the absolutepattern, and therefore the light-receiving arrays PA1, PA2 of thelight-receiving array PA corresponding thereto comprise a plurality(nine, for example, in this embodiment) of light-receiving elements p1,p2 arranged side by side along the measurement direction C (line Lcp) soas to respectively receive the light reflected by the reflection slit saof the slit track SA correspondingly associated thereto. This pluralityof light-receiving elements p1, p2 handles whether or not light isreceived as a bit as described above, and represents the absoluteposition of nine bits in total. Consequently, a light reception signalreceived by each of the plurality of light-receiving elements p1, p2 ishandled independently in the position data generating part 130, and theabsolute position encrypted (coded) into a serial bit pattern is decodedfrom the combination of these light reception signals. The lightreception signal of the light-receiving arrays PA1, PA2 is referred toas an “absolute signal.” Note that, in a case where an absolute patternthat differs from that in this embodiment is used, the light-receivingarrays PA1, PA2 become a configuration corresponding to that pattern.

The light-receiving arrays PI1, PI2 comprise a plurality oflight-receiving elements arranged side by side along the measurementdirection C (line Lcp) so as to respectively receive light reflected bythe reflection slits si1, si2 of the slit tracks SI1, SI2correspondingly associated thereto. First, the light-receiving array isexplained using the light-receiving array PI1 as an example.

According to this embodiment, sets of a total of four light-receivingelements (represented by “SET1” in FIG. 5) are arranged side by side inone pitch (one pitch in the projected image; that is, ε×P1) of theincremental pattern of the slit track SI1, and sets of the fourlight-receiving elements are further arranged side by side in aplurality along the measurement direction C. Then, since the incrementalpattern forms reflection slits repeatedly on a per pitch basis, each ofthe light-receiving elements generates a periodic signal of one period(referred to as 360° in terms of electric angle) in one pitch when thedisk 110 rotates. Then, since four light-receiving elements are disposedin one set corresponding to one pitch, the light-receiving elementsadjacent to each other in one set detect periodic signals comprising aphase difference of 90° from each other. The respective light receptionsignals are referred to as an A-phase signal, a B-phase signal (with aphase difference of 90° from the A-phase signal), a bar A-phase signal(with a phase difference of 180° from the A-phase signal), and a barB-phase signal (with a phase difference of 180° from the B-phasesignal).

The incremental pattern represents a position in one pitch, andtherefore the signal in each phase in one set and the signal in eachphase in another set corresponding thereto have values that change inthe same manner. Consequently, the signals in the same phase are addedacross a plurality of sets. Consequently, from a large number oflight-receiving elements of the light-receiving array PI1 shown in FIG.5, four signals shifted from one another by a phase of 90° are detected.

On the other hand, the light-receiving array PI2 is also configured inthe same manner as the light-receiving array PI1. That is, sets of atotal of four light-receiving elements (represented by “SET2” in FIG. 5)are arranged side by side in one pitch (one pitch in the projectedimage; that is, ε×P2) of the incremental pattern of the slit track SI2,and sets of four light-receiving elements are arranged side by side in aplurality along the measurement direction C. Consequently, four signalsshifted from one another by a phase of 90° are respectively generatedfrom the light-receiving arrays PI1, PI2. These four signals arereferred to as “incremental signals.” Further, the incremental signalsgenerated from the light-receiving array PI2 corresponding to the slittrack SI2 with a short pitch are referred to as “high incrementalsignals” since the resolution is high compared to other incrementalsignals, and the incremental signals generated by the light-receivingarray PI1 corresponding to the slit track SI1 with a long pitch arereferred to as “low incremental signals” since the resolution is lowcompared to other incremental signals.

Note that while this embodiment describes an illustrative scenario inwhich four light-receiving elements are included in one setcorresponding to one pitch of the incremental pattern, the number oflight-receiving elements in one set is not particularly limited thereto,such as a case where two light-receiving elements are included in oneset, for example.

2-3. Position Data Generating Part

The position data generating part 130 acquires two absolute signals,each comprising the bit pattern representing the absolute position, andhigh incremental signals and low incremental signals that include foursignals shifted from one another by a phase of 90°, from the opticalmodule 120, at the timing in which the absolute position of the motor Mis measured. Then, based on the acquired signals, the position datagenerating part 130 calculates the absolute position of the motor Mrepresented by these signals, and outputs position data representing thecalculated absolute position to the controller CT.

Note that, as for the method for generating the position data by theposition data generating part 130, various methods can be used withoutparticular limitation. As an example, the following describes a casewhere the absolute position is calculated from the high incrementalsignal and the low incremental signal as well as the absolute signal,and the position data is then generated.

As shown in FIG. 6, the position data generating part 130 comprises anabsolute position specifying part 131, a first position specifying part132, a second position specifying part 133, and a position datacalculating part 134. The absolute position specifying part 131binarises each absolute signal from the light-receiving arrays PA1, PA2,and converts the signals into bit data representing the absoluteposition. Then, the absolute position specifying part 131 specifies theabsolute position based on the correspondence relationship betweenpredefined bit data and the absolute position.

On the other hand, of the low incremental signals of the respective fourphases from the light-receiving array PI1, the first position specifyingpart 132 subtracts the low incremental signals with a phase differenceof 180° from each other. By subtracting the signals with a phasedifference of 180°, it is possible to cancel out the manufacturingerrors, measurement errors, and the like of the reflection slit withinone pitch. As described above, the signals resulting from thesubtraction are referred to as a “first incremental signal” and a“second incremental signal” here. The first incremental signal and thesecond incremental signal comprise a phase difference of 90° from eachother by electric angle (simply referred to as “A-phase signal,”“B-phase signal,” and the like). Then, the first position specifyingpart 132 specifies a position within one pitch from these two signals.The method for specifying a position within one pitch is notparticularly limited. For example, in a case where the low incrementalsignal, which is a periodic signal, is a sinusoidal signal, an exampleof the above described specification method is to calculate an electricangle φ by performing the arc tangent operation on the result ofdivision of the two sinusoidal signals in the A phase and B phase. Or,there is also a method for converting the two sinusoidal signals into anelectric angle φ using a tracking circuit. Or, there is also a methodfor specifying an electric angle φ correspondingly associated with thevalues of signals in the A phase and B phase in a table created inadvance. At this time, it is preferable for the first positionspecifying part 132 to convert the two sinusoidal signals in the A phaseand B phase from analogue to digital on a per detection signal basis.

The position data calculating part 134 superimposes the position withinone pitch specified by the first position specifying part 132 onto theabsolute position specified by the absolute position specifying part131. With this arrangement, it is possible to calculate an absoluteposition with higher resolution than an absolute position based on anabsolute signal. According to this embodiment, the resolution of thiscalculated absolute position agrees with the number of slits of the slittrack SI2 with a short pitch. That is, in this example, the resolutionof the calculated absolute position is two times the resolution of anabsolute position based on an absolute signal.

On the other hand, the second position specifying part 133 performs thesame processing as the aforementioned first position specifying part 132on the high incremental signals from the light-receiving array PI2, andspecifies a highly accurate position within one pitch from the twosignals. Then, the position data calculating part 134 superimposes theposition within one pitch specified by the second position specifyingpart 133 onto the absolute position calculated based on theaforementioned low incremental signals. With this arrangement, it ispossible to calculate an absolute position that has even higherresolution than the absolute position calculated based on lowincremental signals.

The position data calculating part 134 performs multiplicationprocessing on the absolute position thus calculated to further improvethe resolution, and outputs the result as position data representing ahighly accurate absolute position to the controller CT. The method forspecifying a high resolution absolute position from a plurality ofposition data with different resolutions in this manner is referred toas the “stacking-up method.”

3. Examples of Advantages of this Embodiment

According to this embodiment, the encoder 100 comprises the slit trackSI2 comprising one incremental pattern, and the slit track SI1comprising an incremental pattern that is longer in pitch than the otherincremental pattern. Then, the light-receiving array PI2 is configuredto receive the light reflected by the slit track SI2, and thelight-receiving arrays PI1 is configured to receive the light reflectedby the slit track SI1 with a long pitch. That is, the encoder 100comprises a plurality of types of slit tracks SI1, SI2, each comprisingan incremental pattern that differs in pitch, and a plurality oflight-receiving arrays PI1, PI2 configured to receive the lighttherefrom. With this arrangement, it is possible to generate positiondata representing a high-resolution absolute position by themultiplication stacking-up method that stacks up the multiplicationprocessing of the signal of the light-receiving array PI1 and themultiplication processing of the signal of the light-receiving arrayPI2, thereby making it possible to achieve high resolution.

Further, as described above, in order to stack up the multiplicationprocessing of the signal of the light-receiving array PI1 and themultiplication processing of the signal of the light-receiving array PI2to increase the resolution of the encoder 100, it is necessary toposition both of the light-receiving arrays PI1, PI2 with high accuracyin order to make the phases of the signals of both of thelight-receiving arrays PI1, PI2 agree.

According to this embodiment, the light-receiving array PI1 and thelight-receiving array PI2 are disposed further on the direction sidewhere the light source 121 rather than the light-receiving array PA isdisposed. With this arrangement, it is possible to dispose thelight-receiving array PI1 and the light-receiving array PI2 in closeproximity, thereby making the alignment when forming both of thelight-receiving arrays PI1, PI2 on the substrate BA and when positioningthe optical module 120 with respect to the disk 110 extremely easy,significantly improving the fabricability of the encoder 100. Further,compared to a case where both of the light-receiving arrays PI1, PI2 areseparated, the effect by mechanical displacement resulting fromattachment errors (eccentricity of the disk 110, etc.) and manufacturingerrors is decreased, making it possible to enhance the robustness withrespect to mechanical displacement.

Further, in particular, according to this embodiment, the followingadvantages are achieved. As shown in FIG. 7, a large amount of minuteunevenness exists on the surface of a material 111 of the disk 110,which causes the light emitted from the light source 121 to produceirregular reflection (scattering) when reflected by the disk 110.

FIG. 8 conceptually shows an example of the shape of a convex part 112in the minute unevenness of the material 111. Note that, in FIG. 8, thelength of each arrow of the irregular reflection component representsthe size of intensity. In the example shown in FIG. 8, the convex part112 comprises an upper surface 112 a, and an inclined side surface 112 bthat surrounds the circumference of the upper surface 112 a. The uppersurface 112 a, with its relatively flat shape, has a large surface areawhere the incident light is irradiated diagonally from above (thepositive side along the Y axis and the positive side along the Z axis inthis example), but the side surface 112 b, being slanted, has a smallsurface area where the incident light is irradiated. As a result, theintensity of the irregular reflection component produced by the incidentlight is relatively high for a frontward scattering component Lf, anupward scattering component Lu, and a rearward scattering component Lbscattered by the upper surface 112 a, and relatively low for a sidewaysscattering component Ls scattered by the side surface 112 b in thecircumferential direction, as shown in FIG. 8. Further, of the frontwardscattering component Lf, the upward scattering component Lu, and therearward scattering component Lb, the intensity of the frontwardscattering component Lf scattered in the regular reflection direction ishighest, and the intensity of upward scattering component Lu scatteredupward and the rearward scattering component Lb scattered in thedirection reverse from the advancing direction of the incident light isintermediate (higher than the sideways scattering component Ls).Consequently, the distribution of the irregular reflection components asa whole is dominant in the direction along the Y-Z plane.

FIG. 9 shows the intensity distribution of the irregular reflectioncomponents as viewed from the positive direction along the X axis, andFIG. 10 shows the intensity distribution of the irregular reflectioncomponents as viewed from the positive direction along the Z axis. Notethat the length of each arrow in FIG. 9 and the distance from point E inFIG. 10 represent the size of intensity, respectively. Due to theirregular reflection by the aforementioned convex part 112, theintensity distribution of the irregular reflection components on thesurface of the disk 110 where a large number of minute convex parts 112exists forms a shape that is longer in the direction along the planewhich includes the advancing direction of the light (the Y-Z plane inthis example), and comprises directivity in the direction along the Yaxis as a whole, as shown in FIG. 9 and FIG. 10. More specifically, asshown in FIG. 10, this intensity distribution of the irregularreflection components is a substantially 8-shaped distribution whereintwo circles arranged side by side in the advancing direction of thelight are connected, with the reflection position E as the center, andthe circle on the advancing direction far side of the light inparticular forms a distribution shape that is larger than the circle onthe advancing direction near side. That is, in a case where twolight-receiving arrays are disposed in the same direction, with thelight source 121 as reference in the optical module 120, crosstalk inwhich, for example, the scattered light in the reflection light thatshould reach one light-receiving array reaches the other light-receivingarray, occurs between both light-receiving arrays, causing noise. Then,the light-receiving array that is farther away from the light source 121receives a greater amount of irregular reflection components of thelight than the light-receiving array that is closer to the light source121, sometimes producing even greater noise.

On the other hand, in general, the absolute signal output from thelight-receiving array PA that receives the light reflected by the slittrack SA comprising an absolute pattern is not a repetition signal(sinusoidal, etc.), unlike the incremental signal, making it difficultto reduce the noise resulting from the irregular reflection componentsof the light to be received by the light-receiving array PA beingreceived by another light-receiving array by a filter. As a result, itis preferable to avoid the travel of noise from the light-receivingarray PA to other light-receiving arrays, to the extent possible.

According to this embodiment, the light-receiving array PI1 and thelight-receiving array PI2 are disposed further on the direction sidewhere the light source 121 rather than the light-receiving array PA isdisposed. That is, the light-receiving array PI1 and the light-receivingarray PI2 are not disposed on the extended line of the segment thatconnects the light source 121 and the light-receiving array PA on thelight-receiving array PA side. Consequently, based on the intensitydistribution of the irregular reflection components of the light, it ispossible to suppress the travel of noise from the light-receiving arrayPA to the light-receiving array PI1 and the light-receiving array PI2,making it possible to increase the reliability of the encoder 100.

Further, in particular, according to this embodiment, the followingadvantages are achieved. That is, in the absolute signal output from thelight-receiving array PA that receives the light reflected by the slittrack SA comprising an absolute pattern, the bit pattern resulting fromdetection or non-detection by each of the plurality of light-receivingelements uniquely represents an absolute position. On the other hand, inthe incremental signal output from the light-receiving arrays PI1, PI2,the detection signals resulting from the plurality of light-receivingelements corresponding in phase are added together to represent aposition within one pitch. In terms of the properties of such signals,the light-receiving arrays PI1, PI2 have a relatively high resistance tonoise since the noise is averaged, whereas the light-receiving array PAhas a relatively low resistance to noise. Then, in a case where an LEDor the like is used as the light source 121, galvanic noise light thatdoes not change temporally occurs near the light source 121.

According to this embodiment, the light source 121 is disposed betweenthe light-receiving array PI1 and the light-receiving array PI2. Withthis arrangement, it is possible to dispose the light-receiving arraysPI1, PI2 having high resistance to noise in a position near the lightsource 121 while disposing the light-receiving array PA having lowresistance to noise in a position away from the light source 121.Consequently, it is possible to suppress the effect of the noiseresulting from the aforementioned galvanic noise light to a minimum.

Further, in particular, according to this embodiment, the followingadvantages are achieved. That is, in general, with the light-receivingarray disposed away from the light source, the amount of received lightis reduced. When the light-receiving surface area is increased in orderto maintain the amount of received light, the junction capacitance ofthe respective light-receiving elements increases, decreasing signalresponsiveness. Further, if the amount of received light is reduced,signal responsiveness similarly decreases even if the gain is increasedon the circuit side.

On the other hand, in a case where the multiplication processing of thesignal of the light-receiving array PI1 and the multiplicationprocessing the signal of the light-receiving array PI2 are stacked up asin this embodiment, the accuracy of the final absolute position of theencoder 100 is relatively highly affected by the responsiveness of thesignal output from the light-receiving array PI2. Consequently, thedisposed position of the light-receiving array PI2 is an importantfactor in accuracy improvement. According to this embodiment, the lightsource 121 is disposed between the light-receiving array PI1 and thelight-receiving array PI2. With this arrangement, the light-receivingarray PI2 having a relatively large effect on the accuracy of theabsolute position can be arranged near the light source 121, making itpossible to improve responsiveness. Further, the amount of receivedlight of the light-receiving array PI2, which requires accuracy, can beincreased, making it possible to improve the accuracy of the absoluteposition.

Further, in particular, according to this embodiment, the followingadvantages are achieved. That is, in a case where an LED or the like isused as the light source 121, the light source 121 may comprise lightdistribution characteristics with high directivity. In such a case, theamount of reflection light (light intensity) changes relatively greatlyin the area near the circumference of the light source 121, but thechange in the amount of reflection light is relatively small in the areaon the outside thereof. Then, in the light-receiving array PA thatoutputs an absolute signal, a bit pattern resulting from detection ornon-detection by each of the plurality of light-receiving elementsuniquely represents an absolute position. In terms of the properties ofsuch a signal, if the amount of received light of the respectivelight-receiving elements varies, erroneous detection of the absoluteposition readily occurs, and thus the amount of received light of therespective light-receiving elements is preferably uniform, and thelight-receiving array PA is preferably disposed in an area where thereis small change in the amount of light.

According to this embodiment, the light source 121 is disposed betweenthe light-receiving array PI1 and the light-receiving array PI2. Withthis arrangement, it is possible to separate the light-receiving arrayPA from the light source 121 and dispose it in the aforementioned areawhere there is small change in the amount of light. As a result, it ispossible to increase the reliability of the absolute signal output fromthe light-receiving array PA.

Further, the light source 121 is disposed between the light-receivingarray PI1 and the light-receiving array PI2, making it possible todispose the light-receiving array PI1 and the light-receiving array PI2so that they are practically symmetrical, sandwiching the light source121. As a result, in such a case where the optical module 120 isdisplaced in the rotating direction with the light source 121 as thecenter, or the disk 110 is arranged in an eccentric manner with respectto the shaft SH, the phase of the signal of one of the light-receivingarrays PI1, PI2 advances, and the phase of the signal of the other isdelayed. The amounts of shift in these phases are equal to each other,making it possible to correct the phases of the signals of both of thelight-receiving arrays PI1, PI2 when the multiplication stacking-upprocess is performed. Consequently, even in a case where the opticalmodule 120 is displaced in the rotating direction, or the disk 110 isarranged in an eccentric manner, it is possible to prevent a decrease inthe accuracy of the position data.

Further, in particular, according to this embodiment, only thelight-receiving array PI2 is disposed on the outer circumference side ofthe light source 121. With this arrangement, the width directiondimension is not regulated in the adjacent light-receiving array PA asin the light-receiving array PI1, making it possible to lengthen thewidth direction dimension of the light-receiving array PI2 to a greaterdegree than the other light-receiving array PI1. As a result, the amountof received light of the light-receiving array PI2 that determinesresolution can be increased, making it possible to improve detectionaccuracy.

Further, in particular, according to this embodiment, the followingadvantages are achieved. That is, the detection error resulting from theeccentricity of the disk 110 generally tends to be dependent on theradius of the slit track, increasing when the radius is small anddecreasing when the radius is large.

According to this embodiment, the light-receiving array PI2 is disposedon the outer circumference side, making it possible to increase theradius of the slit track SI2 corresponding to the light-receiving arrayPI2 of the disk 110 the most. Consequently, the detection errorresulting from the eccentricity of the light-receiving array PI2 can bedecreased, and the robustness with respect to the eccentricity can beenhanced. Further, there is also the advantage that the pitch of theslit track SI2 corresponding to the light-receiving array PI2 can bemaintained as large as possible.

4. Modifications

The above has described in detail an embodiment while referring toaccompanying drawings. Nevertheless, the spirit and the scope of thepresent disclosure set forth in the claims are not limited to theembodiment described above. The fact that various changes,modifications, and combinations can be extrapolated within the truespirit and scope will be apparent to persons with ordinary skill in theart affiliated with the embodiments. Consequently, any techniquesresulting from these changes, modifications, and combinations are alsonaturally affiliated with the spirit and scope of the disclosure.

4-1. Disposing the Light-Receiving Array PA on the Outer CircumferenceSide

While the above described embodiment has described an illustrativescenario in which the light-receiving array PA is disposed on the innercircumference side with respect to the light-receiving arrays PI1, PI2(the center axis side), the light-receiving array PA may be disposed onthe outer circumference side with respect to the light-receiving arraysPI1, PI2 (the side opposite the center axis), as shown in FIG. 11, forexample. That is, in this case, the light source 121 and the respectivelight-receiving arrays are disposed in the order of the light-receivingarray PA, the light-receiving array PI2, the light source 121, and thelight-receiving array PI1, from the outside toward the inside in thewidth direction R. Although not shown, in this case, the three slittracks are disposed in the order of SI1, SI2, SA, from the inside towardthe outside in the width direction R on the disk 110. The configurationin the above described embodiment is preferably adopted in a case wherethe width direction dimension of the light-receiving array PI2 is to belengthened, and this configuration is preferably adopted in a case wherethe width direction dimension of the light-receiving array PI1 is to belengthened to increase the amount of received light.

4-2. Disposing the Light-Receiving Array PI1 Further on the OuterCircumference Side than the Light Source

While the above described embodiment has described an illustrativescenario in which the light-receiving array PI1 is disposed on the innercircumference side with respect to the light source 121, thelight-receiving array PI1 may be disposed on the outer circumferenceside with respect to the light source 121, as shown in FIG. 12, forexample. That is, in this case, the light source 121 and the respectivelight-receiving arrays are disposed in the order of the light-receivingarray PI1, the light source 121, the light-receiving array PI2, and thelight-receiving array PA, from the outside toward the inside in thewidth direction R. Although not shown, in this case, the three slittracks are disposed in the order of SA, SI2, SI1, from the inside towardthe outside in the width direction R on the disk 110. The configurationin the above described embodiment is preferably adopted in a case wherethe robustness with respect to the eccentricity of the high incrementalsignal is to be enhanced, and this configuration is preferably adoptedin a case where the robustness with respect to the eccentricity of thelow incremental signal is to be enhanced.

4-3. Disposing the Light-Receiving Array PI1 on the Outer CircumferenceSide, and the Light-Receiving Array PA on the Outer Circumference Side

While the above described modification (4-2) has described anillustrative scenario in which the light-receiving array PA is disposedon the inner circumference side with respect to the light-receivingarrays PI1, PI2, the light-receiving array PA may be disposed on theouter circumference side with respect to the light-receiving arrays PI1,PI2, as shown in FIG. 13, for example. That is, in this case, the lightsource 121 and the respective light-receiving arrays are disposed in theorder of the light-receiving array PA, the light-receiving array PI1,the light source 121, and the light-receiving array PI2, from theoutside toward the inside in the width direction R. Although not shown,in this case, the three slit tracks are disposed in the order of SI2,SI1, SA, from the inside toward the outside in the width direction R onthe disk 110. The configuration in the above described modification(4-2) is preferably adopted in a case where the width directiondimension of the light-receiving array PI1 is to be lengthened, and thisconfiguration is preferably adopted in a case where the width directiondimension of the light-receiving array PI2 is to be lengthened toincrease the amount of received light.

4-4. Disposing the Light Source Between the Light-Receiving Arrays PI1,PI2 and the Light-Receiving Array PA

While the above described embodiment has described an illustrativescenario in which the light source 121 is disposed between thelight-receiving array PI1 and the light-receiving array PI2, the lightsource 121 may be disposed between the light-receiving arrays PI1, PI2and the light-receiving array PA, as shown in FIG. 14, for example.According to this modification, the light source 121 and the respectivelight-receiving arrays are disposed in the order of the light-receivingarray PI2, the light-receiving array PI1, the light source 121, and thelight-receiving array PA, from the outside toward the inside in thewidth direction R. Although not shown, in this case, the three slittracks are disposed in the order of SA, SI1, SI2, from the inside towardthe outside in the width direction R on the disk 110.

In a case where this configuration is adopted, the mechanical robustnesscan be further enhanced. That is, according to this modification, as aresult of the light source 121 being disposed between thelight-receiving arrays PI1, PI2 and the light-receiving array PA, thelight source 121 is not disposed between the light-receiving array PI1and the light-receiving array PI2, making it possible to dispose thelight-receiving array PI1 and the light-receiving array PI2 in closerproximity to each other. As a result, it is possible to further improvethe fabricability of the encoder 100, and further enhance the robustnesswith respect to mechanical displacement, such as attachment errors andmanufacturing errors.

Further, in a case where this configuration is adopted, it is possibleto enhance the robustness with respect to eccentricity. That is,according to this modification, the light-receiving array PI2 isdisposed on the outermost circumference side, making it possible toincrease the radius of the slit track SI2 corresponding to thelight-receiving array PI2 of the disk 110 the most. Consequently, thedetection error resulting from the eccentricity of the light-receivingarray PI2 can be decreased, and the robustness with respect to theeccentricity can be enhanced. Further, there is also the advantage thatthe pitch of the slit track SI2 corresponding to the light-receivingarray PI2 can be maintained as large as possible.

4-5. Disposing the Light-Receiving Array PI1 on the Outer CircumferenceSide

While the above described modification (4-4) has described anillustrative scenario in which the light-receiving array PI1 is disposedon the inner circumference side with respect to the light-receivingarray PI2, the light-receiving array PI1 may be disposed on the outercircumference side with respect to the light-receiving array PI2, asshown in FIG. 15, for example. That is, in this case, the light source121 and the respective light-receiving arrays are disposed in the orderof the light-receiving array PI1, the light-receiving array PI2, thelight source 121, and the light-receiving array PA, from the outsidetoward the inside in the width direction R. Although not shown, in thiscase, the three slit tracks are disposed in the order of SA, SI2, SI1,from the inside toward the outside in the width direction R on the disk110. The configuration in the above described modification (4-4) ispreferably adopted in a case where the robustness with respect to theeccentricity of the high incremental signal is to be enhanced, and thisconfiguration is preferably adopted in a case where the robustness withrespect to the eccentricity of the low incremental signal is to beenhanced.

4-6. Disposing the Light-Receiving Array PA on the Outer CircumferenceSide

While the above described modification (4-4) has described anillustrative scenario in which the light-receiving array PA is disposedon the inner circumference side with respect to the light-receivingarrays PI1, PI2, the light-receiving array PA may be disposed on theouter circumference side with respect to the light-receiving arrays PI1,PI2, as shown in FIG. 16, for example. That is, in this case, the lightsource 121 and the respective light-receiving arrays are disposed in theorder of the light-receiving array PA, the light source 121, thelight-receiving array PI2, and the light-receiving array PI1, from theoutside toward the inside in the width direction R. Although not shown,in this case, the three slit tracks are disposed in the order of SI1,SI2, SA, from the inside toward the outside in the width direction R onthe disk 110.

In a case where this configuration is adopted, it is possible to improvethe responsiveness of the light-receiving array PI2. That is, generally,with the light-receiving array disposed away from the point lightsource, the amount of received light decreases, making it necessary toincrease the light-receiving surface area in order to maintain theamount of received light, but the junction capacitance of the respectivelight-receiving elements increases when the light-receiving surface areais increased, resulting in the problem of a decrease in signalresponsiveness. Further, while the gain can be increased on the circuitside in a case where the amount of received light decreases, the problemarises that signal responsiveness similarly decreases in this case aswell.

According to this modification, the multiplication processing of theincremental signals is performed in two stages as described above, andthe number of multiplications of the light-receiving array PI2 is higherthan the number of multiplications of the light-receiving array PI1,making the signal responsiveness required in the light-receiving arrayPI2 relatively high. By disposing such the light-receiving array PI2near the vicinity of the light source 121, it is possible to maintainthe amount of received light and secure high signal responsiveness.Further, the amount of received light of the light-receiving array PI2increases, making signal processing easier.

4-7. Disposing the Light-Receiving Array PI1 Further on the OuterCircumference Side than the Light-Receiving Array PI2

While the above described modification (4-6) has described anillustrative scenario in which the light-receiving array PI1 is disposedfurther on the inner circumference side than the light-receiving arrayPI2, the light-receiving array PI1 may be disposed further on the outercircumference side than the light-receiving array PI2, as shown in FIG.17, for example. That is, in this case, the light source 121 and therespective light-receiving arrays are disposed in the order of thelight-receiving array PA, the light source 121, the light-receivingarray PI1, and the light-receiving array PI2, from the outside towardthe inside in the width direction R. Although not shown, in this case,the three slit tracks are disposed in the order of SI2, SI1, SA, fromthe inside toward the outside in the width direction R on the disk 110.The configuration in the above described modification (4-6) ispreferably adopted in a case where the robustness with respect to theeccentricity of the high incremental signal is to be enhanced, and thisconfiguration is preferably adopted in a case where the robustness withrespect to the eccentricity of the low incremental signal is to beenhanced.

4-8. Disposing the Light-Receiving Array PA of Two Tracks

While the above described embodiment and the above modification havedescribed illustrative scenarios in which the light-receiving elementsp1, p2 respectively included in the light-receiving arrays PA1, PA2 arealternately disposed along the measurement direction C, therebyconfiguring the two light-receiving arrays PA1, PA2 as thelight-receiving array PA of a single track, the light-receiving array PAmay be configured as the light-receiving arrays PA1, PA2 of two tracksdisposed practically symmetrically, sandwiching the light source 121.

As shown in FIG. 18, according to this modification, four slit tracksare arranged on the upper surface of the disk 110 in the widthdirection. The four slit tracks are concentrically disposed in the orderof SA1, SI1, SI2, SA2, from the inside toward the outside in the widthdirection R. A plurality of reflection slits sa1, sa2, respectivelyincluded in the slit tracks SA1, SA2, is disposed along the entirecircumference of the disk 110 so as to comprise an absolute pattern inthe measurement direction C.

Note that, according to this modification, the same absolute patternsare offset from each other by, for example, a length equivalent toone-half of one bit in the measurement direction C, forming the two slittracks SA1, SA2. This offset amount is a value corresponding to, forexample, half a pitch P1 of a reflection slit si1 of the slit track SI1.With this arrangement, similar to the aforementioned embodiment, theabsolute position is calculated using the detection signal from the slittrack SA2 or the opposite operation is performed when, for example, theabsolute position by the slit track SA1 corresponds to a change point inthe bit pattern. As a result, it is possible to improve the detectionaccuracy of the absolute position. Note that, while the amount ofreceived light in the two light-receiving arrays PA1, PA2 needs to beuniform in the case of such a configuration, according to thismodification, the two light-receiving arrays PA1, PA2 are disposedsubstantially equidistant from the light source as described later,making it possible to achieve the above described configuration.

Note that, instead of offsetting the respective absolute patterns of theslit tracks SA1, SA2 against each other, the light-receiving arrays PA1,PA2 respectively corresponding to the slit tracks SA1, SA2 may be offsetagainst each other in the measurement direction C without offsetting theabsolute patterns, for example.

As shown in FIG. 19, the light-receiving array of the optical module 120in this modification is disposed correspondingly to each of the fourslit tracks SA1, SA2, SI1, SI2. The light-receiving array PA1 isconfigured to receive the light reflected by the slit track SA1, and thelight-receiving array PA2 is configured to receive the light reflectedby the slit track SA2. The light-receiving arrays PI1, PI2 are the sameas those in the aforementioned embodiment.

The light-receiving arrays PA1, PA2 corresponding to the absolutepattern are disposed sandwiching the light source 121 in the widthdirection R. In this example, the light-receiving array PA1 is disposedon the inner circumference side, and the light-receiving array PA2 isdisposed on the outer circumference side. According to this embodiment,the distances between each of the light-receiving arrays PA1, PA2 andthe light source 121 are practically equal. That is, the light-receivingarrays PA1, PA2 are basically formed into an axisymmetrical shape withthe line on the width direction R and the line on the measurementdirection C that pass through the light source 121 as the axes ofsymmetry (excluding the curved shape with the measurement center Os asthe center). Then, the plurality of light-receiving elements included inthe light-receiving arrays PA1, PA2 is arranged side by side at acertain pitch along the measurement direction C (the line Lcp). Thelight-receiving arrays PA1, PA2 respectively receive the reflectionlight from the slit tracks SA1, SA2, thereby generating an absolutesignal comprising a bit pattern in the number of light-receivingelements. Note that the light-receiving arrays PA1, PA2 each correspondto one example of the third light-receiving array, and also to oneexample of means for receiving light reflected by the slit trackcomprising an absolute pattern.

Then, the light-receiving arrays PI1, PI2 are disposed between thelight-receiving arrays PA1, PA2, and the light source 121 is disposedbetween the light-receiving array PI1 and the light-receiving array PI2.As a result, the light source 121 and the respective light-receivingarrays are disposed in the order of the light-receiving array PA2, thelight-receiving array PI2, the light source 121, the light-receivingarray PI1, and the light-receiving array PA1, from the outside towardthe inside in the width direction R.

In a case where this configuration is adopted, it is possible toincrease the intensity of the absolute signal, in addition to the sameadvantages as the above described embodiment, thereby making it possibleto improve the position detection accuracy and increase resistance tovibration, etc.

4-9. Disposing the Light-Receiving Array PI1 Further on the OuterCircumference Side than the Light-Receiving Array PI2

While the above described modification (4-8) has described anillustrative scenario in which the light-receiving array PI1 is disposedfurther on the inner circumference side than the light-receiving arrayPI2, the light-receiving array PI1 may be disposed further on the outercircumference side than the light-receiving array PI2, as shown in FIG.20, for example. That is, in this case, the light source 121 and therespective light-receiving arrays are disposed in the order of thelight-receiving array PA2, the light-receiving array PI1, the lightsource 121, the light-receiving array PI2, and the light-receiving arrayPA1, from the outside toward the inside in the width direction R.Although not shown, in this case, the four slit tracks are disposed inthe order of SA1, SI2, SI1, SA2, from the inside toward the outside inthe width direction R on the disk 110. The configuration in the abovedescribed modification (4-8) is preferably adopted in a case where therobustness with respect to the eccentricity of the high incrementalsignal is to be enhanced, and this configuration is preferably adoptedin a case where the robustness with respect to the eccentricity of thelow incremental signal is to be enhanced. [0100]

4-10. Disposing the Light-Receiving Arrays PI1, PI2 Further on the OuterCircumference Side than the Light-Receiving Array PA

While the above described modifications (4-8) (4-9) have describedillustrative scenarios in which the light-receiving arrays PI1, PI2 aredisposed between the light-receiving arrays PA1, PA2, thelight-receiving arrays PI1, PI2 may be disposed on the outside of thelight-receiving arrays PA1, PA2, as shown in FIG. 21, for example.According to this modification, the light-receiving arrays PI1, PI2 aredisposed on the outer circumference side of the light-receiving arraysPA1, PA2. That is, in this case, the light source 121 and the respectivelight-receiving arrays are disposed in the order of the light-receivingarray PI2, the light-receiving array PI1, the light-receiving array PA2,the light source 121, and the light-receiving array PA1, from theoutside toward the inside in the width direction R. Although not shown,in this case, the four slit tracks are disposed in the order of SA1,SA2, SI1, SI2, from the inside toward the outside in the width directionR on the disk 110. The configuration in this modification can be adoptedin a case where there is a desire to arrange the light-receiving arraysPA1, PA2 near the light source 121 to increase the amount of receivedlight.

Note that while FIG. 21 has shown a case where the light-receiving arrayPI1 is disposed on the inner circumference side with respect to thelight-receiving array PI2, the light-receiving array PI1 may be disposedon the outer circumference side with respect to the light-receivingarray PI2 (not shown) in a case where the robustness with respect to theeccentricity of the low incremental signal is to be enhanced (notshown).

4-11. Disposing the Light-Receiving Arrays PI1, PI2 Further on the InnerCircumference Side than the Light-Receiving Array PA

While the above described modification (4-10) has described anillustrative scenario in which the light-receiving arrays PI1, PI2 aredisposed on the outer circumference side of the light-receiving arraysPA1, PA2, the light-receiving arrays PI1, PI2 may be disposed on theinner circumference side of the light-receiving arrays PA1, PA2, asshown in FIG. 22, for example. In this case, the light source 121 andthe respective light-receiving arrays are disposed in the order of thelight-receiving array PA2, the light source 121, the light-receivingarray PA1, the light-receiving array PI2, and the light-receiving arrayPI1, from the outside toward the inside in the width direction R.Although not shown, in this case, the four slit tracks are disposed inthe order of SI1, SI2, SA1, SA2, from the inside toward the outside inthe width direction R on the disk 110. The configuration in the abovedescribed modification (4-10) is adopted in a case where the robustnesswith respect to the eccentricity of the incremental signal is to beenhanced, and the configuration in this modification is adopted in acase where the robustness with respect to the eccentricity of theabsolute signal is to be enhanced.

Note that while FIG. 22 has shown a case where the light-receiving arrayPI1 is disposed on the inner circumference side with respect to thelight-receiving array PI2, the light-receiving array PI1 may be disposedon the outer circumference side with respect to the light-receivingarray PI2 (not shown) in a case where the robustness with respect to theeccentricity of the low incremental signal is to be enhanced (notshown).

4-12. Other

While the above has described a case where the two slit tracks SI1, SI2comprising incremental patterns that differ in pitch are disposed on thedisk 110, three or more slit tracks comprising incremental patterns thatdiffer in pitch may be disposed. In this case as well, it is possible toachieve high resolution by the stacking-up method. At this time, it isalso possible to use at least one of the light-receiving arrays PA1, PA2for the incremental signal, for example.

Further, while the above has described a case where each of thelight-receiving arrays PA1, PA2 comprises nine light-receiving elements,and the absolute signal represents the absolute position of nine bits,the number of light-receiving elements may be a number other than nine,and the number of bits of the absolute signal is also not limited tonine. Further, the number of the light-receiving elements of thelight-receiving arrays PI1, PI2 is also not particularly limited to thenumber according to the above described embodiment.

Further, while the above has described a case where the encoder 100 isdirectly connected to the motor M, the encoder 100 may be connected viaanother mechanism, such as a reduction device, rotating directionconverter, or the like, for example.

What is claimed is:
 1. An encoder, comprising: a plurality of slittracks that respectively comprise a plurality of reflection slitsarranged along a measurement direction; a point light source configuredto emit diffusion light to the plurality of slit tracks; a firstlight-receiving array configured to receive light reflected by the slittrack comprising an incremental pattern; a second light-receiving arrayconfigured to receive light reflected by the slit track comprising anincremental pattern longer in pitch than other incremental patterns; anda third light-receiving array configured to receive light reflected bythe slit track comprising an absolute pattern, and wherein the firstlight-receiving array and the second light-receiving array are disposedat positions further on a direction side where the point light source isdisposed rather than where the third-light receiving array is disposed.2. The encoder according to claim 1, wherein: the point light source isdisposed between the arrays consisting of the first light-receivingarray and the second light-receiving array, and the thirdlight-receiving array.
 3. The encoder according to claim 1, wherein: themeasurement direction is a circumferential direction with a center axisas the center; and the point light source and the first to thirdlight-receiving arrays are disposed in the order of the firstlight-receiving array, the second light-receiving array, the point lightsource, and the third light-receiving array, toward the center axis froman outer portion in a radial direction of a circle.
 4. The encoderaccording to claim 2, wherein: the measurement direction is acircumferential direction with a center axis as the center; and thepoint light source and the first to third light-receiving arrays aredisposed in the order of the first light-receiving array, the secondlight-receiving array, the point light source, and the thirdlight-receiving array, toward the center axis from an outer portion in aradial direction of a circle.
 5. The encoder according to claim 1,wherein: the measurement direction is a circumferential direction with acenter axis as the center; and the point light source and the first tothird light-receiving arrays are disposed in the order of the thirdlight-receiving array, the point light source, the first light-receivingarray, and the second light-receiving array, toward the center axis froman outer portion in a radial direction of a circle.
 6. The encoderaccording to claim 2, wherein: the measurement direction is acircumferential direction with a center axis as the center; and thepoint light source and the first to third light-receiving arrays aredisposed in the order of the third light-receiving array, the pointlight source, the first light-receiving array, and the secondlight-receiving array, toward the center axis from an outer portion in aradial direction of a circle.
 7. The encoder according to claim 1,wherein: the point light source is disposed between the firstlight-receiving array and the second light-receiving array.
 8. Theencoder according to claim 7, wherein: the measurement direction is acircumferential direction with a center axis as the center; and thepoint light source and the first to third light-receiving arrays aredisposed in the order of the first light-receiving array, the pointlight source, the second light-receiving array, and the thirdlight-receiving array, toward the center axis from an outer portion in aradial direction of a circle.
 9. The encoder according to claim 7,wherein: the measurement direction is a circumferential direction with acenter axis as the center; and the point light source and the first tothird light-receiving arrays are disposed in the order of the thirdlight-receiving array, the first light-receiving array, the point lightsource, and the second light-receiving array, toward the center axisfrom an outer portion in a radial direction of a circle.
 10. The encoderaccording to claim 1, wherein: the third light-receiving array isconfigured as a light-receiving array of two tracks disposed so as to bepractically symmetrical, sandwiching the point light source.
 11. Theencoder according to claim 1, wherein: the point light source, the firstlight-receiving array, the second light-receiving array, and the thirdlight-receiving array are disposed on one substrate.
 12. An encoder,comprising: a plurality of slit tracks that respectively comprise aplurality of reflection slits arranged along a measurement direction; apoint light source configured to emit diffusion light to the pluralityof slit tracks; a first light-receiving array configured to receivelight reflected by the slit track comprising an incremental pattern; asecond light-receiving array configured to receive light reflected bythe slit track comprising an incremental pattern longer in pitch thanother incremental patterns; a third light-receiving array configured toreceive light reflected by the slit track comprising an absolutepattern; and one substrate where the point light source, the firstlight-receiving array, and the second light-receiving array aredisposed, and wherein the first light-receiving array and the secondlight-receiving array are disposed at positions further on a directionside where the point light source is disposed rather than where thethird-light receiving array is disposed on the substrate.
 13. Anencoder, comprising: a plurality of slit tracks that respectivelycomprise a plurality of reflection slits arranged along a measurementdirection; means for emitting diffusion light to the plurality of slittracks; first means for receiving light reflected by the slit trackcomprising an incremental pattern; second means for receiving lightreflected by the slit track comprising an incremental pattern longer inpitch than other incremental patterns; and third means for receivinglight reflected by the slit track comprising an absolute pattern, andwherein the first means and the second means are disposed at positionsfurther on a direction side where the means for emitting diffusion lightis disposed rather than where the third means is disposed.
 14. A motorwith an encoder, comprising: a linear motor wherein a mover moves withrespect to a stator, or a rotary motor wherein a rotor rotates withrespect to a stator; and the encoder according to claim 1 configured todetect at least one of a position and a velocity of the mover or therotor.
 15. A motor with an encoder, comprising: a linear motor wherein amover moves with respect to a stator, or a rotary motor wherein a rotorrotates with respect to a stator; and the encoder according to claim 12configured to detect at least one of a position and a velocity of themover or the rotor.
 16. A servo system comprising: a linear motorwherein a mover moves with respect to a stator, or a rotary motorwherein a rotor rotates with respect to a stator; the encoder accordingto claim 1 configured to detect at least one of a position and avelocity of the mover or the rotor; and a controller configured tocontrol the linear motor or the rotary motor based on a detection resultof the encoder.
 17. A servo system comprising: a linear motor wherein amover moves with respect to a stator, or a rotary motor wherein a rotorrotates with respect to a stator; the encoder according to claim 12configured to detect at least one of a position and a velocity of themover or the rotor; and a controller configured to control the linearmotor or the rotary motor based on a detection result of the encoder.